A nickel brazing sheet currently available is an amorphous sheet formed by quenching rolling of a molten metal having a composition of a nickel brazing filler metal. A spring-like elasticity of such an amorphous sheet makes it difficult to fit and fill the sheet in a predetermined space. In addition, since the sheet is an extremely thin foil (several tens of micrometers thick), good workability cannot be expected. In order to fill a large space, it is required to cut the foils in a predetermined shape, and lay the foils to form multi layers on a joint surface. Furthermore, a limitation on sheet width restricted by a nozzle diameter used in the quenching rolling method also inhibits the workability. In order to braze a joint having a large width, it is necessary to lay a plurality of the brazing sheets adjacent to each other.
In addition to the brazing sheets, a powder of a nickel brazing filler metal is also available. However, with such a powder, good workability during the brazing operation also cannot be expected, because it is required to mix a binder with a powder to form a paste, and a process for vaporization of the binder cannot be avoided before brazing. In addition, some carbonized binder remains after brazing and deteriorates the quality of the brazing joint.